A Combination Method of Liquid Hot Water and Phosphotungstic Acid Pretreatment for Improving the Enzymatic Saccharification Efficiency of Rice Straw

Thermodynamic modeling of freeze pretreatment in the destruction of rice straw structure combined with alkaline-hydrothermal method for enzymatic hydrolysis

Freeze pretreatment combined with alkaline-hydrothermal method of rice straw for enzymatic hydrolysis was studied. Crystallization stress in the rice stem pores caused by water freezing at -20- -40 °C was modeled to illustrate the destruction mechanism. The stress was calculated as 22.5-38.3 MPa that were higher than the tensile yield stress of untreated stems (3.0 MPa), indicating ice formation damaging pore structure. After freeze at -20 °C, rice straw was further hydrothermally treated at 190 °C with 0.4 M Na2CO3, achieving 72.0 % lignin removal and 97.2 % cellulose recovery. Glucose yield rose to 91.1 % by 4.3 times after 24 h hydrolysis at 10 FPU loading of Cellic®CTec2 cellulase. The specific surface area of rice straw was 2.6 m2/g increased by 1.2 times after freeze. Freeze combined with alkaline-hydrothermal treatment is a green and energy-efficient method for improving enzymatic hydrolysis.

Biological Conversion of Agricultural Wastes into Indole-3-acetic Acid by Streptomyces lavenduligriseus BS50-1 Using a Response Surface Methodology (RSM)

Agricultural waste is an alternative source for plant growth regulator biosynthesis by microorganisms. Actinobacteria are important soil microbes that significantly impact the soil as plant growth-promoting rhizobacteria and biofertilizers. This study focused on developing low-cost medium based on bagasse to improve indole-3-acetic acid (IAA) production by Streptomyces lavenduligriseus BS50-1 using a response surface methodology (RSM). Among 34 actinobacterial strains, S. lavenduligriseus BS50-1 produced the highest IAA level within the selected medium. An RSM based on a central composite design optimized the appropriate nutrients for IAA production. Thus, glucose hydrolysate and l-tryptophan at concentrations of 3.55 and 5.0 g/L, respectively, were the optimal factors that improved IAA production from 37.50 to 159.47 μg/mL within 168 h. This study reported a potential application of leftover bagasse as the raw material for cultivating actinobacteria, which efficiently produce IAA to promote plant growth.

A Value-Added Utilization Method of Sugar Production By-Products from Rice Straw: Extraction of Lignin and Evaluation of Its Antioxidant Activity

To value-added utilization of the rice straw, two types of lignin were extracted from the by-products of sugar production. The ether-extracted lignin with a purity of 98.7% was extracted from the pretreatment filtrate with two times the concentrated filtrate volume of ether, where the lignin yield was 6.62 mg/g of the rice straw. The ball-milled lignin with a purity of 99.6% was extracted from the milled enzymatic hydrolysis residue with a 1,4-dioxane solution, where the revolution speed and grinding time were 300 rpm and 12 h, respectively. The yield of ball-milled lignin was 34.52 mg/g of the rice straw, which was 421.5% higher than that extracted from extract-free rice straw. In the process of rice straw pretreatment and lignin extraction, 76.43% by mass of phosphotungstic acid catalyst and approximately 98% by volume of 1,4-dioxane solution could be recycled and reused. Compared with the soda lignin extracted from papermaking black liquor, the scavenging rates of DPPH radical and ABTS+ radical of ether-extracted lignin increased by 36.26% and 41.18%, respectively, while the above scavenging rates of ball-milled lignin increased by 30.22% and 37.75%, respectively. Moreover, the reducing power of the two extracted lignins was also stronger than that of soda lignin. The ether-extracted lignin and ball-milled lignin have the potential to be developed as natural macromolecular antioxidants.